Intraluminal, intracavity, intravascular, and intracardiac treatments and diagnosis of medical conditions utilizing minimally invasive procedures are effective tools in many areas of medical practice. These procedures are typically performed using imaging and treatment catheters that are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated, such as the femoral artery. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which is used to locate and diagnose a diseased portion of the body, such as a stenosed region of an artery. For example, U.S. Pat. No. 5,368,035, issued to Hamm et al., the disclosure of which is incorporated herein by reference, describes a catheter having an intravascular ultrasound imaging transducer.
FIG. 1a shows an example of an imaging transducer assembly 1 known in the art. The imaging transducer 1 is typically within the lumen 60 of a guidewire (partially shown), having an outer tubular wall member 5. The imaging transducer assembly 1 includes a coaxial cable 110, having a center conductor wire 120 and an outer shield wire 140, shown in FIG. 1b. A conductive wire, having a diameter of approximately 500 microns, is wrapped around the coaxial cable 110, forming a coil, which functions as a drive shaft 10. Connected to the distal end of the drive shaft 10 is a stainless steel housing 20, which serves to reinforce the structure of the imaging transducer assembly 1. Surrounding the coaxial cable 110, within the housing 20 is a silver epoxy 30, a conductive material. Thus, the housing 20 is electrically coupled to the shield wire 140 of the coaxial cable 110 via the epoxy 30. On the distal end of the silver epoxy 140 is an insulating substance, a non-conductive epoxy 35.
On the distal end of the non-conductive epoxy 35 is a layer of piezoelectric crystal (“PZT”) 80, “sandwiched” between a conductive acoustic lens 70 and a conductive backing material 90, formed from an acoustically absorbent material (e.g., an epoxy substrate having tungsten particles). The acoustic lens 70 is electrically coupled with the center conductor wire 120 of the coaxial cable 110 via a connector 40 that is insulated from the silver epoxy 30 and the backing material 90 by the non-conductive epoxy 35. The backing material 90 is connected to the steel housing 20. It is desirable for the imaging transducer assembly 1 to be surrounded by a sonolucent media. Thus, the lumen 60 of the guidewire is also filled with saline around the assembly 1. The driveshaft 10, the housing 20, and the acoustic lens 70 are exposed to the saline. During operation, the PZT layer 80 is electrically excited by both the backing material 90 and the acoustic lens 70. The backing material 90 receives its charge from the shield wire 140 of the coaxial cable 110 via the silver epoxy 30 and the steel housing 30, and the acoustic lens 70, which may also be silver epoxy, receives its charge from the center conductor wire 120 of the coaxial cable 110 via the connector 40, which may be silver epoxy as well.
Turning to FIG. 1c, the imaging transducer assembly 1 can be depicted as a simple electric circuit having a voltage source 150, two terminals, A and B, a load 81 caused by the saline filled in the lumen 60, and the PZT load 80. The saline load 81 and the PZT load 80 are charged by the voltage source 150 via the two terminals, A and B, representing the shield wire 140 and the center conductor wire 120 of the coaxial cable 110, respectively. In addition, transducer control circuitry (not shown), which may include a signal processor to handle imaging signals, may also be coupled with the transducer assembly 1.
The imaging transducer is an effective tool for obtaining the cross-sectional image of a blood vessel. However, in some instances, it may be desirable to obtain more information, such as a three-dimensional longitudinal profile of the same blood vessel in addition to the cross-sectional image. Accordingly, an improved imaging transducer assembly would be desirable.